1. Field of the Invention
The present invention relates to screen-printing plates, a method for manufacturing laminated-ceramic electronic devices in a process of laminating ceramic green sheets provided with electrode patterns formed by using the screen-printing plate, and a laminated-ceramic electronic device manufactured by the method.
2. Description of the Related Art
Generally, laminated-ceramic electronic devices are manufactured in processes of laminating and contact-bonding a predetermined number of ceramic green sheets provided with a plurality of internal electrode patterns formed by printing or applying electrode paste, cutting the laminated ceramic sheets into individual elements, and firing the elements.
In accordance with recent advances in miniaturization of electronic apparatuses, the laminated-ceramic electronic devices have been reduced in size and been improved in performance. In particular, a laminated-ceramic capacitor has a trend toward a larger number of laminations, in which the lamination of internal electrodes and dielectrics is increased to achieve miniaturization and larger capacity.
However, when intending to increase the number of laminations of the internal electrodes and the dielectrics and when a predetermined number of ceramic green sheets provided with the internal electrode patterns are contact-bonded to each other, a problem has been found in that regions in which the internal electrode patterns are provided and the regions in which the internal electrode patterns are not provided differ in level, or height, from each other, whereby defects of the internal structure, such as delamination, are likely to be produced.
The above difference in level is produced by laminating the ceramic green sheets provided with the internal electrode patterns. However, the difference in level is not caused only by providing the internal electrode patterns, and is sometimes produced also by variations in the coating thickness between each internal electrode pattern.
Therefore, it is also an important task to reduce the variations in the coating thickness between the internal electrode patterns in order to reduce the difference in level and to increase the number of laminations.
Hitherto, a screen-printing method has been used for printing electrode paste on a ceramic green sheet. As shown in FIGS. 7 and 8, in the screen-printing method, a screen-printing plate 51 provided with a plurality of mesh holes 62 so as to form a plurality of printing patterns 61 is disposed on a ceramic green sheet 52, electrode paste 53 is supplied onto the screen-printing plate 51, and a squeegee 54 is moved in a predetermined direction, for example, in a direction of an arrow Y in FIG. 7 while the squeegee 54 is pressed onto the screen-printing plate 51, whereby the electrode paste 53 passes through the mesh holes 62 forming the printing patterns 61 of the screen-printing plate 51, the electrode paste 53 is printed on the ceramic green sheet 52, and predetermined electrode patterns 55 are formed.
However, in the above screen-printing method, tension is not applied evenly to the overall screen-printing plate 51 when the squeegee 54 is moved while being pressed. Effective pressure applied to the printing patterns 61 in a region R1 disposed in the vicinity of the periphery and close to a frame 56 tends to become greater than the effective pressure applied to the printing patterns 61 in a central region R2 which is disposed separated from the frame 56, as shown in FIG. 8. Therefore, the screen-printing plate 51 tends to expand more in the region R1 close to the periphery than in the central region R2. As a result, the coating of the electrode pattern 55 becomes thinner in the region R1 close to the periphery than in the central region R2, and there occurs a problem in that variations in the coating thickness of a plurality of the electrode patterns 55 printed by using one screen-printing plate 51 are produced. The problem is that the variations in the coating thickness have an unfavorable effect regarding the production of difference in level of the ceramic green sheets after laminated and contact-bonded.
A related technology is known, which is a method in which the sizes of mesh holes in a single printing pattern, which is formed by providing the mesh holes in a screen-printing plate, are made different from each other (refer to, for example, Japanese Unexamined Patent Application Publication No. 6-349663). However, the fact is that any effective method has not been developed particularly for avoiding variations in the coating thickness between a plurality of the electrode patterns 55, as described above, which are printed by using the screen printing plate 51 provided with a plurality of printing patterns in a plate frame of the screen printing plate 51.